The present invention relates to the general field of thrusters for delivering thrust for driving aerospace vehicles such as missiles, launchers, or indeed satellites, using the principle of propulsion by reaction or by ejecting gas. The invention relates more precisely to the fixed-throat nozzles fitted to solid propellant thrusters.
A solid propellant thruster is mainly constituted by a shell containing a block of powder (propellant), an ignitor, and a nozzle with a fixed diverging portion. The block of powder is pierced by a channel lying on the axis of the thruster that acts as a combustion chamber. The ignitor ignites the powder at one end of the shell and combustion of the propellant propagates from the front towards the rear of the thruster. The powder burns at a predefined rate, thereby producing combustion gas that is expelled via the nozzle.
The throat section of the nozzle makes it possible to control the combustion of the block of powder so as to maintain a desired pressure in the combustion chamber while producing the expected thrust. Thus, for a thruster delivering thrust at a single discharge rate, the throat section of the nozzle is unvarying and predetermined as a function of the desired level of thrust.
Nevertheless, having recourse to a single unvarying throat section is not suitable for a thruster that has two rates of operation (typically a high discharge rate and a low discharge rate).
In order to mitigate such a drawback, it is known to provide the nozzle with a throat section that is variable. In practice, a needle that is movable in translation is received inside the nozzle. The position of the needle in the flow of combustion gas serves to determine the flow section for the gas passing through the nozzle, thereby adjusting the gas ejection section to the operating rate of the thruster.
Nevertheless, variable throat section thrusters known in the prior art do not enable the thrust coefficients to be optimized both during a stage of operation at a high level of pressure in the thruster (corresponding to a high discharge rate) and during a stage of operation at a lower level of pressure in the thruster (corresponding to operating at a low discharge rate).